LEAD SCREW ASSEMBLY

A leadscrew assembly comprising: a screw shaft (1) along which is formed a first helical groove (10); a primary nut (2) along which is form a second helical groove (20); the first helical groove and the second helical groove cooperating to define a track (10,20); a secondary nut (5) along which is formed a third helical groove (30); the first helical groove and the third helical groove cooperating to define a track (10, 30) with a nominal running clearance; a preload X is provided wherein when a load applied to the screw exceeds the predetermined preload, the secondary nut engages with the track such that load of the screw above preload X is transferred through the secondary nut and thus protecting the primary nut.